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Old 10-02-2013, 07:03   #1
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Yanmar Overheating

Yesterday, Yanmar 3GM30-93 (on 36' SV) overheated. We had been under power for 2 hrs, towing inflatable dinghy, headed into 20 knot winds with 4-6 foot building waves. Running at 2900-3000 rpm. Stopped, let cool. Checked everything. Oil, belts, leaks, etc. Nothing obvious. Impeller for water relaced last year. Approx 200 hrs on engine since then. I assume this was caused due to strain/resistance on engine. Restarted and powered to port at 2000 rpm (long, slow trip). No further overheating problem.
BUT, what else do/should I check to be sure all is OK? Any suggestions ate welcome. Thanks.

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Old 10-02-2013, 07:26   #2
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Re: Yanmar Overheating

I have a Yanmar 3GM30F. I run it at 2550-2600 for up to 10-12 hours a day when cruising. I've been told that running it at 2800 or above should only be done for short periods. I'm not an expert by any stretch of the imagination, so I offer that for what it's worth. I've never had an overheating problem, even in conditions a bit worse than what you describe.

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Old 10-02-2013, 07:35   #3
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Re: Yanmar Overheating

Did you check the filter for the intake water? We sucked up some little shad once filling the filter trap and overheating the engine. Cleaning the filter was relatively easy, but we had to get to a marina to backflush the foot of line or so leading to the filter, which itself had clogged with fish.
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Old 10-02-2013, 07:42   #4
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Re: Yanmar Overheating

Check the obvious first, Sea Strainer and hoses. It sounds like you are back at the dock, so check water flow at the exhuast.

The less obivous are the impeller, which will sometimes fail at less than 200 hours and the heat exchanger, which could be getting some growth inside it, resisticting water flow at higher RPMs

With that said, if you were motoring into heavy seas, towing a dinghy, at high RPMs for that egnine, you probabaly over heated it from the drag on the boat.

I think the Max RPMs on that engine is 3200? So normally you would run no more than 80% of max RPM or about 2560 rpm.
Tom Jeremiason
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Old 10-02-2013, 07:53   #5
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Re: Yanmar Overheating

Definitely too much load caused by the conditions at that RPM, items to check have already been covered... Back off the throttle when you see it rising past where you are comfortable.... A circulating running diesel cools way faster than a stopped diesel...
In the harsh marine environment, something is always in need of repair...

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Old 10-02-2013, 07:54   #6
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Re: Yanmar Overheating

Yes, the manual says full throttle for one hour max. Could have been so close to full throttle in those conditions for two hours, that caused the problem.

Seem to remember full time cruise RPM is around 2700, though not sure without looking. My personal limit on cruise RPM is 2500 for a 3gm30f.

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